This invention relates to ambient room illumination responsive thermostat control apparatus and particularly to such apparatus for automatically changing the temperature response level of a thermostat for the conventional heating system during predetermined periods of the day.
The various enclosed and inhabited structures such as homes, institutions, commercial buildings and the like, are heated and cooled to create a comfortable temperature.
Generally, thermostatic controls include a temperature-responsive switch element located within a thermostat housing which is constructed to expose the element to the ambient room temperature. Adjustable means permit setting of the response temperature level for actuating the switch at a predetermined, sensed ambient temperature. The switch element opens and closes the connection of a pair of thermostat control leads which run through the wall of the structure directly to a system controller and are connected in series to the control elements.
An adjustable thermostat connected to control the heating and/or cooling system permits the inhabitants to select the temperature desired for comfort. In some installations, a plurality of zone heating systems will be employed with individual thermostats in the several areas for separately controlling the temperature. For example, a home may be conveniently divided into various areas or zones and individually controlled in accordance with the normal usage.
Although the commercially available thermostats are often provided with manually adjusted, temperature setting controls, various automatic devices have also been suggested to affect an automatic adjustement of the temperature setting to eliminate the necessity for manual monitoring of the settings and to provide automatic control in the absence of the personnel. In particular, such devices have been widely employed to affect the automatic setback of temperature during night-time hours when the requirement for heating is significantly reduced.
The interest in such an automatic control device has recently increased as a result of questioning of the availability of energy sources, the cost factors of the available energy and the like. Various methods have, over the years, been suggested. For example, U.S. Pat. No. 1,597,773 disloses a clock-operated unit for providing an automatic temperature setback at a selected night setting in combination with an electrical operator connected in circuit with the lighting system to permit overriding thereof when the lights are turned on.
British Pat. No. 1,005,175, discloses a system which was particularly adapted to a horticultural building and relies on a solar energy responsive device located on the roof structure or the like to control the setting of the mean temperature to be maintained by the heating or cooling means and thereby permit controlling of the conditions within the horticultural glass house. U.S. Pat. No. 3,834,614 discloses a method in which a clock-operated mechanism operates an auxiliary heating source to establish a false heat flow over the normal thermostat unit during the night periods. This auxiliary heat inhibits operation of the heating system unless the normal ambient temperature drops further than can be replaced by the auxiliary heat source.
A more typical commercially available type of system is generally shown in U.S. Pat. No. 3,891,144 which employs a clock-operated day-night switching system. The clock system is driven directly by a series connection to the thermostat control leads with an appropriate circuit employing a coupling resistor provided to maintain continous energization of the clock even though all sensing circuits are open. The resistor of course results in a voltage drop and correspondingly reduces the available voltage to the sytem controller. The control must of course therefore be specially constructed to compensate for such voltage drop; requiring either a special clock, increased voltage or the like to insure a high degree of accuracy.
Although, therefore, many different suggestions have heretofore been developed, there remains a distinct need for a simple, reliable and relatively inexpensive automatic setting change apparatus which can be incorporated into a thermostat control unit with present system specifications for affecting an automatic setback and/or which can be incorporated into an existing installation.